With the recent popularization of computers, an inkjet printer is widely used for printing letters or images on paper, film, cloth or the like not only at offices but also at homes.
The inkjet recording method includes a system of ejecting a liquid droplet by applying a pressure using a piezoelectric element, a system of ejecting a liquid droplet by generating a bubble in ink by heat, a system of using an ultrasonic wave, and a system of ejecting a liquid droplet by drawing by an electrostatic force. The ink composition used for such inkjet recording methods includes an aqueous ink, an oily ink and a solid (melt-type) ink. Among these inks, the aqueous ink becomes mainstream in view of production, handleability, odor, safety and the like.
The coloring agent used in such an ink for ink-jet recording method is required to have high solubility in a solvent, enable high-density recording, have good color hue, exhibit excellent fastness to light, heat, air, water and chemicals, ensure good fixing property and less blurring on an image-receiving material, provide ink having excellent storability, shows no toxicity, have high purity, and be available at a low cost. However, it is very difficult to find out a coloring agent satisfying these requirements in a high level. Although various dyes and pigments for inkjet recording method have been already proposed and actually used, a coloring agent satisfying all requirements is not yet found out at present. Conventionally well-known dyes and pigments having a Colour Index (C.I.) number can hardly satisfy both color hue and fastness required of the ink for inkjet recording method. Various studies have been made on dyes having both good color hue and fastness with an attempt to develop a dye excellent as the coloring agent for inkjet recording method. However, a water-soluble group is necessarily substituted on a compound as a water-soluble dye. When the number of water-soluble groups is increased so as to improve the stability of ink, it has been found to cause a problem in that the image formed is readily blurred under high-humidity conditions.